Italian Patent 1 278 633, European Patent 0 733 820 and U.S. Pat. No. 5,706,922 have disclosed a transmission and torque-limiting joint able to disengage the driven member from the driving member upon exceeding a maximum value of the transmitted torque and to allow recoupling at a lesser value of the relative velocity; one of the two members is outer and the other inner. Provided on the inner surface of the outer member are receptive recesses and in the inner member at least two tangential seats, each extending orthogonally to a radial direction and lying parallel in a plane orthogonal to the axis of a rotation of the joint; in correspondence with each of said tangential seats, a radial glide seat is provided, extending between the periphery of said inner member and the tangential seat; in each of said tangential seats two opposing gliding pads elastically stressed toward one another and having opposing surfaces with receptive symmetrical shapings are provided; in said radial glide seat a slider with a wedge-shaped inner profile is accommodated, able to glide centripetally and to penetrate between the two pads, thus parting them, and with a shaped outer profile able to cooperate with one or other of said receptive recesses of the outer member, so as to transmit a torque between said two members, inner and outer, and to generate a centripetal radial thrust on the wedge-shaped element, which thrust increases with the increase in the transmitted torque until it causes the separation of the two pads with the aid of the wedge-shaped profile of the slider and the centripetal movement of said slider until it frees the latter from the recess in which it was captive. The reverse movements of the sliders, with the aid of the elastic urgings on the pads, are obtained after a reduction in the relative velocity between said two members, driving and driven.
A joint as defined above can engage a in plurality of different angular positions.
In order to obtain coupling in a single angular position,Italian Patent 1 286 703 and International patent WO98/06959 have disclosed a particular solution which provides, in each of said receptive recesses, at least one peg flush with the inner surface of said outer member; furthermore, in each of said plate-like sliders at least one transverse through notch is machined, each notch being sized so as to accommodate one of said pegs. The arrangement of the peg or pegs in each of the various recesses is different from that in the other recesses and corresponds to the arrangement of the notch or notches of one of the sliders only. With these combinations, each slider can penetrate only in the corresponding recess and continues past the other recesses, sliding over their peg or pegs; thus coupling occurs only in one unique reciprocal angular position between the two members of the joint and takes place simultaneously with all sliders in the corresponding recesses.
In the solutions mentioned above, the radial coupling sliders or plugs become damaged and worn - under disengagement conditions because of the very frequent passing of the sliders in front of the recesses, and the continuous elastic stressing of the sliders toward coupling, owing to the action of the springs which act upon each of them.
The present invention solves both the problems of coupling in a single analogous position and the problem of reducing the wear on the elements of the joint, in a particularly simple, reliable and economical manner. These and other objects and advantages will become apparent from the text which follow.
The invention relates to a transmission and torque-limiting joint of the abovementioned type.
According to the invention, said joint possesses substantially the following features:
said substantially radial glide seats in the inner member are disposed at mutually different angles and said recesses being correspondingly arranged in the outer member;
and the elastic means able to urge said sliders in the centrifugal direction comprise two symmetrical discoidal elements, on whose facing surfaces shaped portions are tangentially machined which are able to cooperate with corresponding inner profiles of said sliders, springs being provided capable of stressing said two discoidal elements toward one another.
With this arrangement, said discoidal elements remain spaced apart from one another by the inner profiles of at least two of said sliders, as a result of which the other sliders can move radially in the centrifugal direction without elastic stressings; said discoidal elements, however, are elastically brought into contact with one another only when the two members, driving and driven, of the joint are located in the unique reciprocal angular position in which one recess corresponds to each slider; in this reciprocal angular position, and only in this reciprocal angular position, all the sliders are elastically urged into the respective recesses of the outer member, as a result of which the transmission coupling between positions, the sliders are either retained between the two discoidal elements in an attitude in which they are sheltered in the respective radial glide seats or freely movable in the glide seats and subjected to virtually no damage as a result of the relative angular movement between the two members of the joint, apart from a possible weak centrifugal stressing caused by their own weight.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.